Dr. Schopfer’s research is focused on the understanding of the biological effects of electrophilic fatty acids. In particular, he studies the mechanism by which nitrated fatty acid activate and signal through peroxisome proliferator-activated receptor gamma (PPARγ). This receptor is the target of currently used antidiabetic drugs (thiazolidinediones). The activation of the receptor regulates fat and glucose metabolism, resulting in an overall decrease of glucose levels to normal values in patients with type II diabetes. The targeting of this receptor by nitrated fatty acids results in a decrease of the glucose levels to normal values like thiazolidinediones, but without the known secondary effects exerted by thiazolidinediones. In addition to the intrinsic therapeutic value of nitrated fatty acid, they will aid in the understanding of the biological mechanism involved in PPARγ activation, leading to improved designs of anti-diabetic drugs targeting the PPARγ receptor.

Fig 1. Modeling of PPARγ receptor activation by nitrated oleic acid

Biological effects of endogenous PPARϒ ligands

The role of the PPARγ receptor in diabetes has been well established. Nonetheless, the role of endogenous signaling molecules on the activation of PPARϒ is still unclear and under debate. Nitrated fatty acids are endogenously formed and bind to PPARγ with high affinity rivaling Rosiglitazone (thiazolidinediones), resulting in receptor activation. In addition, nitrated fatty acids covalently modify a critical cysteine (cys285) in the ligand binding pocket of PPARγ promoting a particular conformational change that results in partial receptor activation. This partial activation results in the expression of a particular subset of genes under PPARγ regulation and a biological outcome that differs from the one obtained when activating the receptor with Rosiglitazone. Dr. Schopfer’s work focuses on understanding the mechanism of this selective activation and how it avoids the side effect presented upon full activation by agonist like Rosiglitazone.

Endogenous formation of electrophiles and biological relevance

Electrophilic fatty acids are constantly formed as fatty acid breakdown products during oxidative stress and as signaling messengers by enzymatic or non enzymatic pathways. Dr. Schopfer studies the formation of biologically relevant electrophiles, in particular nitrated fatty acids, and their signaling mechanisms. The study involves the detection and characterization of novel electrophiles formed during inflammation. Once the molecules are characterized, a chemical synthesis approach is used to generate enough quantities for biological experiments.

Electrophiles induce an important cellular response that includes the induction of phase II genes. This will in turn set up a more protective environment against damaging electrophilic molecules. A key player in the initiation of this biological response is the Keap 1/Nrf 2 couple. Keap 1 is usually bound to Nrf 2 in the cytoplasm. Upon formation of electrophiles, Keap 1, which contains several highly reactive cysteine, is targeted, dissociates from Nrf2 and is routed to degradation by the proteosome. These lead to Nrf2 nuclear translocation and activation of phase II genes. In particular, we study the mechanism by which different biologically relevant electrophiles target KEAP 1 and activate Nrf 2 responses. In addition, a more general proteomic approach is use to evaluate and characterize different electrophilic cellular protein targets. Once critical targets are identified using a mass spectrometry approach, a functional study of the modification is performed to determine the relevance and its cellular effects.